Group marriage next, warns MP

COALITION MP Kevin Andrews has warned that legalising same-sex marriage could lead to an acceptance of group marriage.

The Age reported that in his book, Maybe I do: Modern Marriage and the Pursuit of Happiness, released on Thursday, Mr Andrews said the assertion that redefining marriage would not affect other marriages was misplaced.

He wrote that if same-sex unions were recognised by civil law, "other arrangements can also be recognised.

"Once the state can no longer insist that marriage involves a commitment to a member of the opposite sex, there is no ground (other than superstition) for insisting that marriage be limited to one person rather than several".

It was a thorny issue for Opposition Leader Tony Abbot, who forced parliamentary secretary Cory Bernardi to resign over comments made in the Senate suggesting gay marriage could lead to an acceptance of bestiality.

Senator Bernardi also said the next step from having gay marriage was three or four people being able to enter a permanent union.